Systems and methods for improved communication efficiency in high efficiency wireless networks

ABSTRACT

Systems, methods, and devices for wireless communication are described herein. In some aspects, a method of wireless communication includes transmitting a first message for establishing a reservation of the communication medium utilizing a first combination of transmission characteristics such that the first message is readable by a plurality of wireless devices. The method may further include subsequently transmitting a plurality of messages for clearing the reservation of the communication medium, each of the plurality of messages utilizing a different combination of transmission characteristics than the first combination such that each of the plurality of messages is readable by a different subset of the plurality of wireless devices, thereby sequentially clearing access to at least one communication channel of the communication medium for each different subset of the plurality of wireless devices.

CLAIM OF PRIORITY UNDER 35 U.S.C. § 119

This application is a continuation of U.S. patent application Ser. No.14/456,856 filed Aug. 11, 2014, which claims priority under 35 U.S.C. §119 to Provisional Application No. 61/871,785 entitled “SYSTEMS ANDMETHODS FOR IMPROVED COMMUNICATION EFFICIENCY IN HIGH EFFICIENCYWIRELESS NETWORKS” filed Aug. 29, 2013, and assigned to the assigneehereof. U.S. patent application Ser. No. 14/456,856 and ProvisionalApplication No. 61/871,785 are hereby expressly incorporated byreference herein.

FIELD

The present application relates generally to wireless communications,and more specifically to systems, methods, and devices for selectivelyblocking communications in wireless networks.

BACKGROUND

In many telecommunication systems, communications networks are used toexchange messages among several interacting spatially-separated devices.Networks may be classified according to geographic scope, which couldbe, for example, a metropolitan area, a local area, or a personal area.Such networks would be designated respectively as a wide area network(WAN), metropolitan area network (MAN), local area network (LAN), orpersonal area network (PAN). Networks also differ according to theswitching/routing technique used to interconnect the various networknodes and devices (e.g. circuit switching vs. packet switching), thetype of physical media employed for transmission (e.g. wired vs.wireless), and the set of communication protocols used (e.g. Internetprotocol suite, SONET (Synchronous Optical Networking), Ethernet, etc.).

Wireless networks are often preferred when the network elements aremobile and thus have dynamic connectivity needs, or if the networkarchitecture is formed in an ad hoc, rather than fixed, topology.Wireless networks employ intangible physical media in an unguidedpropagation mode using electromagnetic waves in the radio, microwave,infra-red, optical, etc. frequency bands. Wireless networksadvantageously facilitate user mobility and rapid field deployment whencompared to fixed wired networks.

The devices in a wireless network may transmit/receive informationbetween each other. The devices may communicate at different data rates.Where many devices share a communication network and there are largedifferences between the communication rates of the devices network,congestion and inefficient link usage may result. As such, systems,methods, and non-transitory computer-readable media are needed forimproving communication efficiency in high efficiency wireless networks.

SUMMARY

The systems, methods, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention as expressed bythe claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this invention provide advantages that include decreasingthe size of control frames.

One aspect of the disclosure provides a method of wirelesscommunication. The method transmitting a first message for establishinga reservation of the communication medium utilizing a first combinationof transmission characteristics such that the first message is readableby a plurality of wireless devices. The method comprises subsequentlytransmitting a plurality of messages for clearing the reservation of thecommunication medium, each of the plurality of messages utilizing adifferent combination of transmission characteristics than the firstcombination such that each of the plurality of messages is readable by adifferent subset of the plurality of wireless devices, therebysequentially clearing access to at least one communication channel ofthe communication medium for each different subset of the plurality ofwireless devices.

Another aspect of the disclosure provides a device for wirelesscommunication. The device comprises a processor configured to generate afirst message for establishing a reservation of the communication mediumutilizing a first combination of transmission characteristics such thatthe first message is readable by a plurality of wireless devices. Theprocessor is further configured to generate a plurality of messages forclearing the reservation of the communication medium, each of theplurality of messages utilizing a different combination of transmissioncharacteristics than the first combination such that each of theplurality of messages is readable by a different subset of the pluralityof wireless devices. The device further comprises a transmitterconfigured to transmit the first message, thereby establishing thereservation of the communication medium. The transmitter is furtherconfigured to subsequently transmit the plurality of messages, therebysequentially clearing access to at least one communication channel ofthe communication medium for each different subset of the plurality ofwireless devices.

Another aspect of the disclosure provides a non-transitorycomputer-readable medium comprising code that, when executed, causes adevice for wireless communication to transmit a first message forestablishing a reservation of the communication medium utilizing a firstcombination of transmission characteristics such that the first messageis readable by a plurality of wireless devices. The code, when executed,further causes the device to subsequently transmit a plurality ofmessages for clearing the reservation of the communication medium, eachof the plurality of messages utilizing a different combination oftransmission characteristics than the first combination such that eachof the plurality of messages is readable by a different subset of theplurality of wireless devices, thereby sequentially clearing access toat least one communication channel of the communication medium for eachdifferent subset of the plurality of wireless devices.

Another aspect of the disclosure provides a device for wirelesscommunication. The device comprises means for generating a first messagefor establishing a reservation of the communication medium utilizing afirst combination of transmission characteristics such that the firstmessage is readable by a plurality of wireless devices. The devicecomprises means for generating a plurality of messages for clearing thereservation of the communication medium, each of the plurality ofmessages utilizing a different combination of transmissioncharacteristics than the first combination such that each of theplurality of messages is readable by a different subset of the pluralityof wireless devices. The device comprises means for transmitting thefirst message, thereby establishing the reservation of the communicationmedium. The device comprises means for subsequently transmitting theplurality of messages, thereby sequentially clearing access to at leastone communication channel of the communication medium for each differentsubset of the plurality of wireless devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a wireless communication system inwhich aspects of the present disclosure may be employed.

FIG. 2 illustrates various components that may be utilized in a wirelessdevice that may be employed within the wireless communication system ofFIG. 1.

FIG. 3 illustrates an example of a clear to send (CTS)-to-Self frame.

FIG. 4 illustrates an example of a contention free (CF)-end frame.

FIG. 5 illustrates a timing diagram including a CTS-to-Self frame and aCF-end frame as may be utilized within the wireless communication system100.

FIG. 6 illustrates another timing diagram including a CTS-to-Self frameand a sequence of CF-end frames as may be utilized within the wirelesscommunication system 100.

FIG. 7 shows a flow chart of an exemplary method of wirelesscommunication.

DETAILED DESCRIPTION

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. The teachings disclosure may, however, be embodied in manydifferent forms and should not be construed as limited to any specificstructure or function presented throughout this disclosure. Rather,these aspects are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the disclosure to thoseskilled in the art. Based on the teachings herein one skilled in the artshould appreciate that the scope of the disclosure is intended to coverany aspect of the novel systems, apparatuses, and methods disclosedherein, whether implemented independently of or combined with any otheraspect of the invention. For example, an apparatus may be implemented ora method may be practiced using any number of the aspects set forthherein. In addition, the scope of the invention is intended to coversuch an apparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to or otherthan the various aspects of the invention set forth herein. It should beunderstood that any aspect disclosed herein may be embodied by one ormore elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

Wireless network technologies may include various types of wirelesslocal area networks (WLANs). A WLAN may be used to interconnect nearbydevices together, employing widely used networking protocols. Thevarious aspects described herein may apply to any communicationstandard, such as WiFi or, more generally, any member of the IEEE 802.11family of wireless protocols. For example, the various aspects describedherein may be used as part of the IEEE 802.11ah, 801.11ac, 802.11n,802.11g, and/or 802.11b protocols.

In some aspects, wireless signals in a sub-gigahertz band may betransmitted according to the 802.11ah protocol using orthogonalfrequency-division multiplexing (OFDM), direct-sequence spread spectrum(DSSS) communications, a combination of OFDM and DS SS communications,or other schemes. Implementations of the 802.11 ah protocol may be usedfor sensors, metering, and smart grid networks. Advantageously, aspectsof certain devices implementing the 802.11ah protocol may consume lesspower than devices implementing other wireless protocols, such as802.11b and/or 802.11g for example, and/or may be used to transmitwireless signals across a relatively long range, for example about onekilometer or longer.

Certain of the devices described herein may further implement MultipleInput Multiple Output (MIMO) technology. This may also be implemented aspart of the 802.11 ah standard. A MIMO system employs multiple (N_(T))transmit antennas and multiple (N_(R)) receive antennas for datatransmission. A MIMO channel formed by the N_(T) transmit and N_(R)receive antennas may be decomposed into N_(S) independent channels,which are also referred to as spatial channels or streams, whereN_(S)≤min{N_(T), N_(R)}. Each of the N_(S) independent channelscorresponds to a dimension. The MIMO system can provide improvedperformance (e.g., higher throughput and/or greater reliability) if theadditional dimensionalities created by the multiple transmit and receiveantennas are utilized.

In some implementations, a WLAN includes various devices which are thecomponents that access the wireless network. For example, there may betwo types of devices: access points (“APs”) and clients (also referredto as stations, or “STAs”). In general, an AP serves as a hub or basestation for the WLAN and an STA serves as a user of the WLAN. Forexample, an STA may be a laptop computer, a personal digital assistant(PDA), a mobile phone, etc. In an example, an STA connects to an AP viaa WiFi (e.g., IEEE 802.11 protocol such as 802.11ah) compliant wirelesslink to obtain general connectivity to the Internet or to other widearea networks. In some implementations an STA may also be used as an AP.

An access point (“AP”) may also comprise, be implemented as, or known asa NodeB, Radio Network Controller (“RNC”), eNodeB, Base StationController (“BSC”), Base Transceiver Station (“BTS”), Base Station(“BS”), Transceiver Function (“TF”), Radio Router, Radio Transceiver, orsome other terminology.

A station “STA” may also comprise, be implemented as, or known as anaccess terminal (“AT”), a subscriber station, a subscriber unit, amobile station, a remote station, a remote terminal, a user terminal, auser agent, a user device, user equipment, or some other terminology. Insome implementations an access terminal may comprise a cellulartelephone, a cordless telephone, a Session Initiation Protocol (“SIP”)phone, a wireless local loop (“WLL”) station, a personal digitalassistant (“PDA”), a handheld device having wireless connectioncapability, or some other suitable processing device connected to awireless modem. Accordingly, one or more aspects taught herein may beincorporated into a phone (e.g., a cellular phone or smartphone), acomputer (e.g., a laptop), a portable communication device, a headset, aportable computing device (e.g., a personal data assistant), anentertainment device (e.g., a music or video device, or a satelliteradio), a gaming device or system, a global positioning system device,or any other suitable device that is configured to communicate via awireless medium.

As discussed above, certain of the devices described herein mayimplement the 802.11 ah standard, for example. Such devices, whetherused as an STA or AP or other device, may be used for smart metering orin a smart grid network. Such devices may provide sensor applications orbe used in home automation. The devices may instead or in addition beused in a healthcare context, for example for personal healthcare. Theymay also be used for surveillance, to enable extended-range Internetconnectivity (e.g. for use with hotspots), or to implementmachine-to-machine communications.

FIG. 1 illustrates an example of a wireless communication system 100 inwhich aspects of the present disclosure may be employed. The wirelesscommunication system 100 may operate pursuant to a wireless standard,for example at least one of the 802.11ah, 802.11ac, 802.11n, 802.11g and802.11b standards. The wireless communication system 100 may include anAP 104, which communicates with STAs 106.

A variety of processes and methods may be used for transmissions in thewireless communication system 100 between the AP 104 and the STAs 106.For example, signals may be transmitted and received between the AP 104and the STAs 106 in accordance with OFDM/OFDMA techniques. If this isthe case, the wireless communication system 100 may be referred to as anOFDM/OFDMA system. Alternatively, signals may be transmitted andreceived between the AP 104 and the STAs 106 in accordance with CDMAtechniques. If this is the case, the wireless communication system 100may be referred to as a CDMA system.

A communication link that facilitates transmission from the AP 104 toone or more of the STAs 106 may be referred to as a downlink (DL) 108,and a communication link that facilitates transmission from one or moreof the STAs 106 to the AP 104 may be referred to as an uplink (UL) 110.Alternatively, a downlink 108 may be referred to as a forward link or aforward channel, and an uplink 110 may be referred to as a reverse linkor a reverse channel.

The AP 104 may provide wireless communication coverage in a basicservice area (BSA) 102. The AP 104 along with the STAs 106 associatedwith the AP 104 and that use the AP 104 for communication may bereferred to as a basic service set (BSS). It should be noted that thewireless communication system 100 may not have a central AP 104, butrather may function as a peer-to-peer network between the STAs 106.Accordingly, the functions of the AP 104 described herein mayalternatively be performed by one or more of the STAs 106.

FIG. 2 illustrates various components that may be utilized in a wirelessdevice 202 that may be employed within the wireless communication system100. The wireless device 202 is an example of a device that may beconfigured to implement the various methods described herein. Forexample, the wireless device 202 may comprise the AP 104 or one of theSTAs 106.

The wireless device 202 may include a processor 204 which controlsoperation of the wireless device 202. The processor 204 may also bereferred to as a central processing unit (CPU). Memory 206, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 204. A portion of thememory 206 may also include non-volatile random access memory (NVRAM).The processor 204 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 206. Theinstructions in the memory 206 may be executable to implement themethods described herein.

The processor 204 may comprise or be a component of a processing systemimplemented with one or more processors. The one or more processors maybe implemented with any combination of general-purpose microprocessors,microcontrollers, digital signal processors (DSPs), field programmablegate array (FPGAs), programmable logic devices (PLDs), controllers,state machines, gated logic, discrete hardware components, dedicatedhardware finite state machines, or any other suitable entities that canperform calculations or other manipulations of information. In someimplementations, the processor 204 may also be known as, or comprise atleast a portion of means for generating a first message for establishinga reservation of the communication medium utilizing a first combinationof transmission characteristics such that the first message is readableby a plurality of wireless devices. In some implementations, theprocessor 204 may also be known as, or comprise at least a portion ofmeans for generating a plurality of messages for clearing thereservation of the communication medium, each of the plurality ofmessages utilizing a different combination of transmissioncharacteristics than the first combination such that each of theplurality of messages is readable by a different subset of the pluralityof wireless devices.

The processing system may also include machine-readable media forstoring software. Software shall be construed broadly to mean any typeof instructions, whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise. Instructions mayinclude code (e.g., in source code format, binary code format,executable code format, or any other suitable format of code). Theinstructions, when executed by the one or more processors, cause theprocessing system to perform the various functions described herein.

The wireless device 202 may also include a housing 208 that may includea transmitter 210 and a receiver 212 to allow transmission and receptionof data between the wireless device 202 and a remote location. Thetransmitter 210 and receiver 212 may be combined into a transceiver 214.An antenna 216 may be attached to the housing 208 and electricallycoupled to the transceiver 214. The wireless device 202 may also include(not shown) multiple transmitters, multiple receivers, multipletransceivers, and/or multiple antennas, which may be utilized duringMIMO communications, for example. In some implementations, thetransmitter 210 may also be known as, or comprise at least a portion ofmeans for transmitting the first message, thereby establishing thereservation of the communication medium. In some implementations, thetransmitter 210 may also be known as, or comprise at least a portion ofmeans for subsequently transmitting the plurality of messages, therebysequentially clearing access to at least one communication channel ofthe communication medium for each of the different subsets of theplurality of wireless devices.

The wireless device 202 may also include a signal detector 218 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 214. The signal detector 218 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 202 may alsoinclude a digital signal processor (DSP) 220 for use in processingsignals. The DSP 220 may be configured to generate a data unit fortransmission. In some aspects, the data unit may comprise a physicallayer data unit (PPDU). In some aspects, the PPDU is referred to as apacket.

The wireless device 202 may further comprise a user interface 222 insome aspects. The user interface 222 may comprise a keypad, amicrophone, a speaker, and/or a display. The user interface 222 mayinclude any element or component that conveys information to a user ofthe wireless device 202 and/or receives input from the user.

The various components of the wireless device 202 may be coupledtogether by a bus system 226. The bus system 226 may include a data bus,for example, as well as a power bus, a control signal bus, and a statussignal bus in addition to the data bus. Those of skill in the art willappreciate the components of the wireless device 202 may be coupledtogether or accept or provide inputs to each other using some othermechanism.

Although a number of separate components are illustrated in FIG. 2,those of skill in the art will recognize that one or more of thecomponents may be combined or commonly implemented. For example, theprocessor 204 may be used to implement not only the functionalitydescribed above with respect to the processor 204, but also to implementthe functionality described above with respect to the signal detector218 and/or the DSP 220. Further, each of the components illustrated inFIG. 2 may be implemented using a plurality of separate elements.

As discussed above, the wireless device 202 may comprise an AP 104 or anSTA 106, and may be used to transmit and/or receive communications. Thecommunications exchanged between devices in a wireless network mayinclude data units which may comprise packets or frames. In someaspects, the data units may include data frames, control frames, and/ormanagement frames. Data frames may be used for transmitting data from anAP and/or a STA to other APs and/or STAs. Control frames may be usedtogether with data frames for performing various operations and forreliably delivering data (e.g., acknowledging receipt of data, pollingof APs, area-clearing operations, channel acquisition, carrier-sensingmaintenance functions, etc.). Management frames may be used for varioussupervisory functions (e.g., for joining and departing from wirelessnetworks, etc.).

FIG. 3 illustrates an example of a CTS-to-Self frame. The CTS-to-Selfframe 300 may be transmitted by a device to reserve a channel or mediumfor communication. The CTS-to-Self frame 300 includes 4 differentfields: a frame control (FC) field 302, a duration field 304, a receiveraddress (RA) field 306 (also referred to as a receiver address (a1)),and a frame check sequence (FCS) field 308. FIG. 3 further indicates thesize in octets of each of the fields 302, 304, 306 and 308 as 2, 2, 6and 4, respectively. Summing the value of all of the field sizes givesthe overall size of the CTS-to-self frame 300, which is 14 octets. TheRA field 306 includes a full MAC address of a device, which is a 48-bit(6 octet) value. For a CTS-to-Self frame the MAC address in the RA field306 would correspond to the device transmitting the CTS-to-Self frame.Since the CTS-to-Self frame 300 is addressed to the same device thattransmitted it, all other devices able to read (e.g., decode) theCTS-to-Self frame 300 and listening on the communication channel will besilenced for the duration indicated in the duration field 304.

FIG. 4 illustrates a contention free end (CF-end) frame 400. The CF-endframe 400 may be transmitted by a device signaling the end of acontention free period. Thus, the CF-end frame 400 may be used to cancela reservation made in response to a network allocation vector (NAV), forexample, the CTS-to-Self frame 300 of FIG. 3. Any receiver receiving theCF-end frame 400 may then determine any NAV should be canceled. TheCF-end frame 400 includes 5 different fields: a frame control (FC) field402, a duration field 404, a receiver address (RA) field 406 (alsoreferred to as a receiver address (a1)), a transmitter address (TA)field 408 (also referred to as a transmitter address (a2)), and a framecheck sequence (FCS) field 410. FIG. 4 further indicates the size inoctets of each of the fields 402, 404, 406, 408 and 410, as 2, 2, 6, 6,and 4, respectively. Summing the value of all of the field sizes givesthe overall size of the CF-end frame 400, which is 20 octets. Theduration field 404 may be set by the generating STA to 0 to indicate thecompletion of the transmission opportunity (TXOP) (i.e., set the NAV ofthe receiving STAs to 0). Each of the RA and TA fields 406, 408comprises a full MAC address of a device, which is a 48-bit (6 octet)value. Thus, all devices that can read (e.g., decode) the CF-end frame400 listening on the communication channel previously silenced for theduration indicated in the duration field 304 of the CTS-to-Self frame300, for example, will be able to communicate on the communicationchannel again.

FIG. 5 illustrates a timing diagram including a CTS-to-Self frame and aCF-end frame as may be utilized within the wireless communication system100. FIG. 5 shows an exemplary sequence that may be utilized to silenceone or more wireless devices while one or more other wireless devicesare permitted to communicate. The timing diagram 500 shows beacon 502,CTS-to-Self frame 504 and CF-end frame 506. In FIG. 5, the AP 104 ofFIG. 1, for example, may transmit the CTS-to-Self frame 504 to itself.Although the CTS-to-Self frame 504 may be transmitted at any time,transmitting the CTS-to-Self frame 504 near the beacon 502 ensures thatthe STAs, for example STAs 106 a-106 d, are awake when the CTS-to-Selfframe 504 is transmitted. The CTS-to-Self frame 504 may initiate aninterval 520 during which any receiving STAs are silent unless thereceiving STAs receive and read (e.g., decode) a CF-end frame.

The AP 104 may transmit the CTS-to-Self frame 504 using a transmissioncharacteristic such that at least the wireless devices to be silencedcan read (e.g., decode) the CTS-to-Self frame 504. For example, withrespect to FIG. 1, it may be desirable to silence the STAs 106 a, 106 b,and 106 c so that the STA 106 d may communicate with the AP 104 withoutinterference. Thus, the transmission characteristic may be such that atleast the STAs 106 a, 106 b and 106 c may read (e.g., decode) theCTS-to-Self frame 504. When the STAs 106 a-106 c detect the CTS-to-Selfframe 504, the STAs 106 a-106 c will be silenced for the interval 520 asidentified by the duration field within the CTS-to-Self frame 504. Theduration field of the CTS-to-Self frame 504 may be set such that apredetermined percentage of a total communication time is reserved forthe STA 106 d to communicate. The STA 106 d may also be able to read(e.g., decode) the CTS-to-Self frame 504.

The AP 104 may subsequently transmit the CF-end frame 506 using anothertransmission characteristic such that at least one wireless device to becleared for communication, and not the at least one wireless devices tobe silenced, can read (e.g., decode) the CF-end frame 506. The CF-endframe 506 may be transmitted within the duration of the interval 520.For example, the STA 106 d may be able to read (e.g., decode) the CF-endframe 506. Decoding the CF-end frame 506 will clear any silence commandthat may have been invoked by the CTS-to-Self frame 504 for the STA 106d. In this way the AP 104 may clear at least one communication channelfor the STA 106 d. In addition, the AP 104 may repeat transmitting theCTS-to-Self frame 504 and subsequently transmitting the CF-end frame 506according to a periodic interval.

In one implementation, the transmission characteristic may be a physicallayer (PHY) mode. In this implementation, the STAs 106 a-106 c mayinclude PHYs operating in a mode according to the IEEE 802.11b standard.Thus, the STAs 106 a-106 c can read (e.g., decode) messages transmittedutilizing the PHY mode associated with 802.11 ac. By contrast, the STA106 d may have a PHY that operates according to the IEEE 802.11acstandard and, thus, may be able to read (e.g., decode) messagestransmitted utilizing the PHY mode associated with 802.11 ac. In thisimplementation, the AP 104 may transmit the CTS-to-Self frame 504utilizing the PHY mode associated with the 802.11b standard, forexample. Thus, the STAs 106 a-106 c can read (e.g., decode) theCTS-to-Self frame 504 and will be silent for the interval 520. The AP104 may subsequently transmit the CF-end frame 506 utilizing the PHYmode associated with the 802.11ac standard. Since the STAs 106 a-106 coperate utilizing the PHY mode associated with the 802.11b standard theSTAs 106 a-106 c will not be able to read (e.g., decode) the CF-endframe 506 and will remain silent for the interval 530. However, the STA106 d will be able to read (e.g., decode) the CF-end frame 506 and willbe enabled to communicate with the AP 104 without interference from theSTAs 106 a-106 c during the interval 530. In this way, the devicesoperating in particular PHY modes may be blocked in favor of devicesoperating in another PHY mode during the interval 530.

In another implementation, the transmission characteristic may be amodulation coding scheme (MCS). In this implementation, the STAs 106a-106 c may utilize complementary code keying (CCK), for example, andthus, may be able to read (e.g., decode) messages transmitted accordingthe CCK scheme. By contrast, the STA 106 d may utilize orthogonalfrequency-division multiplexing (OFDM) and, thus, may be able to read(e.g., decode) messages transmitted according to the OFDM scheme. Inthis implementation, the AP 104 may transmit the CTS-to-Self frame 504utilizing CCK. Thus, the STAs 106 a-106 c may be able to read (e.g.,decode) the CTS-to-Self frame 504 and will be silent for the interval520. The AP 104 may subsequently transmit the CF-end frame 506 utilizingOFDM. Since the STAs 106 a-106 c operate utilizing the CCK scheme theSTAs 106 a-106 c will not be able to read (e.g., decode) the CF-endframe 506 and will remain silent for the interval 530. However, the STA106 d will be able to read (e.g., decode) the CF-end frame 506 and willbe enabled to communicate without interference from the STAs 106 a-106 cduring the interval 530. In this way, the devices operating under aparticular MCS may be blocked in favor of devices operating underanother MCS during the interval 530.

In yet another implementation, the transmission characteristic may be abandwidth. In this implementation, the STAs 106 a-106 c may communicateutilizing a bandwidth of 20 MHz and, thus, the may be able to read(e.g., decode) messages transmitted utilizing the 20 MHz bandwidth. Bycontrast, the STA 106 d may communicate utilizing bandwidths of any of20 MHz, 40 MHz, 80 MHz and 160 MHz, for example, and thus, may be ableto read (e.g., decode) messages utilizing bandwidths of any of 20 MHz,40 MHz, 80 MHz and 160 MHz. In this implementation, the AP 104 maytransmit the CTS-to-Self frame 504 utilizing a bandwidth of 20 MHz.Thus, the STAs 106 a-106 c may be able to read (e.g., decode) theCTS-to-Self frame 504 and will be silent for the interval 520. The AP104 may subsequently transmit the CF-end frame 506 utilizing a bandwidthof 80 MHz. Since the STAs 106 a-106 c operate utilizing bandwidths of 20MHz the STAs 106 a-106 c will not be able to read (e.g., decode) theCF-end frame 506 and will remain silent for the interval 530. However,the STA 106 d will be able to read (e.g., decode) the CF-end frame 506and will be enabled to communicate without interference from the STAs106 a-106 c during the interval 530. In this way, the devices utilizinga particular bandwidth may be blocked in favor of devices utilizinganother bandwidth during the interval 530.

In yet another implementation, the transmission characteristic may be atransmission frequency. In this implementation, the STAs 106 a-106 c maycommunicate at a frequency of 2.4 GHz and, thus, may be able to read(e.g., decode) messages transmitted at 2.4 GHz. By contrast, the STA 106d may communicate and read (e.g., decode) messages at a frequency of 5GHz, for example. In this example, the AP 104 may transmit theCTS-to-Self frame 504 at a frequency of 2.4 GHz. Thus, the STAs 106a-106 c may be able to read (e.g., decode) the CTS-to-Self frame 504 andwill be silent for the interval 520. The AP 104 may subsequentlytransmit the CF-end frame 506 at a frequency of 5 GHz. Since the STAs106 a-106 c operate at a frequency of 2.4 GHz the STAs 106 a-106 c willnot be able to read (e.g., decode) the CF-end frame 506 and will remainsilent for the interval 530. However, the STA 106 d will be able to read(e.g., decode) the CF-end frame 506 and will be enabled to communicatewithout interference from the STAs 106 a-106 c during the interval 530.In this way, the devices operating at a particular frequency may beblocked in favor of devices operating at another frequency during theinterval 530.

In yet another implementation, the transmission characteristic may be anumber of MIMO streams. In this implementation, the STAs 106 a-106 c maycommunicate and read (e.g., decode) messages utilizing only a singledata stream. By contrast, the STA 106 d may communicate utilizing anynumber of data streams between 1 and 8, for example and thus, the STA106 d may be able to read (e.g., decode) messages transmitted utilizingany number of data streams between 1 and 8. In this example, the AP 104may transmit the CTS-to-Self frame 504 utilizing a single data stream.Thus, the STAs 106 a-106 c may be able to read (e.g., decode) theCTS-to-Self frame 504 and will be silent for the interval 520. The AP104 may subsequently transmit the CF-end frame 506 utilizing 4 MIMO datastreams, for example. Since the STAs 106 a-106 c utilize a single datastream the STAs 106 a-106 c will not be able to read (e.g., decode) theCF-end frame 506 and will remain silent for the interval 530. However,the STA 106 d will be able to read (e.g., decode) the CF-end frame 506and will be enabled to communicate without interference from the STAs106 a-106 c during the interval 530. In this way, the devices onlycapable of operating in a particular MIMO configuration, or withoutMIMO, may be blocked in favor of devices capable of operating at anotherMIMO configuration during the interval 530.

In yet another implementation, the transmission characteristic may be adata rate per stream. In this implementation, the STAs 106 a-106 c maycommunicate and read (e.g., decode) messages utilizing a data rate of 1,2, 5.5 or 11 Mb/s. By contrast, the STA 106 d may communicate and read(e.g., decode) messages at up to more than 800 Mb/s, for example. Inthis implementation, the AP 104 may transmit the CTS-to-Self frame 504at a data rate of 11 Mb/s. Thus, the STAs 106 a-106 c may be able toread (e.g., decode) the CTS-to-Self frame 504 and will be silent for theinterval 520. The AP 104 may subsequently transmit the CF-end frame 506at a data rate of 54 Mb/s, for example. Since the STAs 106 a-106 c maycommunicate at up to only 11 Mb/s the STAs 106 a-106 c will not be ableto read (e.g., decode) the CF-end frame 506 and will remain silent forthe interval 530. The CF-end frame 506 transmitted at 54 Mb/s mayinstead appear as noise to the STAs 106 a-106 c. However, the STA 106 dwill be able to read (e.g., decode) the CF-end frame 506 and will beenabled to communicate without interference from the STAs 106 a-106 cduring the interval 530. In this way, the devices having lowcommunication rates may be blocked in favor of devices having highercommunication rates during the interval 530.

In addition to the exemplary implementations described above, thepresent application contemplates any combination of the above exemplaryimplementations without limitation. For example, the AP 104 may transmitthe CTS-to-Self frame 504 utilizing an MCS compatible with at least theSTAs to be silenced and then transmit the CF-end frame 506 utilizing anumber of MIMO channels compatible with the one or more STAs to becleared for communication and not the STAs to be silenced.

The present inventive concepts need not be limited to a single group ofdevices to be silenced and a single group of devices to be cleared forcommunication. In another implementation, a sequence of CF-end framesmay be transmitted having successively different transmissioncharacteristics in order to allow successive access to a communicationchannel based on STA compatibility with the successively differenttransmission characteristics. In this way, finer grained control of whatdevices are blocked, and during which intervals, may be affected.

FIG. 6 illustrates another timing diagram including a CTS-to-Self frameand a sequence of CF-end frames as may be utilized within the wirelesscommunication system 100. FIG. 6 shows an exemplary sequence that may beutilized to silence one or more wireless devices while a plurality ofother wireless devices are permitted to communicate during successiveintervals based on their compatibility with one or more transmissioncharacteristics. The timing diagram 600 shows beacon 602, CTS-to-Selfframe 604, CF-end frame 606 a, CF-end frame 606 b, and CF-end frame 606c. Although three CF-end frames are shown, the present application isnot so limited and may include any number of CF-end frames. In FIG. 6,an AP, for example the AP 104 of FIG. 1, may transmit the CTS-to-Selfframe 604 to itself. Although the CTS-to-Self frame 604 may betransmitted at any time, transmitting the CTS-to-Self frame 604 near thebeacon 602 ensures that the STAs, for example STAs 106 a-106 d, areawake when the CTS-to-Self frame 604 is transmitted. The CTS-to-Selfframe 604 may initiate an interval 620 during which any receiving STAsare silent.

The AP 104 may transmit the CTS-to-Self frame 604 using a transmissioncharacteristic such that at least the wireless devices to be silencedmay read (e.g., decode) the CTS-to-Self frame 604. For example, withrespect to FIG. 1, it may be desirable to silence the STAs 106 a, 106 b,and 106 c for at least a certain interval so that the STA 106 d maycommunicate with the AP 104 without interference. The AP 2104 maytransmit the CTS-to-Self frame 604 using a transmission characteristicthat at least the STAs 106 a, 106 b and 106 c can read (e.g., decode).Thus, the STAs 106 a-106 c will be silent for the interval 620 asidentified by the duration field within the CTS-to-Self frame 604. TheSTA 106 d may also be able to read (e.g., decode) the CTS-to-Self frame604.

In one implementation, the STA 106 a of FIG. 1 may only be capable ofcommunicating utilizing a single data stream. The STA 106 b may becapable of communicating utilizing either a single data stream or 2 MIMOdata streams. The STA 106 c may be capable of communicating utilizingany number of data streams between 1 and 3. The STA 106 d may be capableof communicating utilizing any number of data streams from 1 to 4. Thus,in this implementation, the AP 104 may transmit the CTS-to-Self frame604 utilizing a single data stream such that each of the STAs 106 a-106d may read (e.g., decode) the CTS-to-Self frame 604 and be silent.

The AP 104 may subsequently transmit the CF-end frame 606 a utilizing 4MIMO data streams. Thus, the STA 106 d will be able to read (e.g.,decode) the CF-end frame 606 a and will be cleared to communicate overthe communication channel in exclusivity for at least the interval 630.Since the STAs 106 a-106 c cannot read (e.g., decode) messagestransmitted utilizing 4 MIMO data streams, the STAs 106 a-106 c cannotread (e.g., decode) the CF-end frame 606 a and will remain silent.

The AP 104 may subsequently transmit the CF-end frame 606 b utilizing 3MIMO data streams. Thus, both the STAs 106 c and 106 d will be able toread (e.g., decode) the CF-end frame 606 b. The STA 106 d has alreadybeen cleared for communication by the CF-end frame 606 a. The STA 106 cwill now be cleared to communicate over the communication channel alongwith the STA 106 d for at least the interval 640. Since the STAs 106a-106 b cannot read (e.g., decode) messages transmitted utilizing 3 MIMOdata streams, the STAs 106 a-106 b cannot read (e.g., decode) the CF-endframe 606 b and will remain silent.

The AP 104 may subsequently transmit the CF-end frame 606 c utilizing 2MIMO data streams. Thus, each of the STAs 106 b-106 d will be able toread (e.g., decode) the CF-end frame 606 c. The STAs 106 c and 106 dhave already been cleared for communication by the CF-end frames 606 band 606 a, respectively. The STA 106 b will now be cleared tocommunicate over the communication channel along with the STAs 106 c and106 d for at least the interval 650, while the STA 106 a will remainsilent.

Although the above implementation utilizes the number of MIMO datachannels as the transmission characteristic, the present application isnot so limited. Other implementations may utilize transmissioncharacteristics including but not limited to, the PHY mode, the MCS, thebandwidth, the transmission frequency, the data rate, or any combinationof those transmission characteristics, similar to that previouslydescribed in connection with FIG. 5. In addition, the AP 104 may repeattransmitting the CTS-to-Self frame 604 and subsequently transmitting thesequence of CF-end frames 606 a-606 c according to a periodic interval.Although the examples described above in connection with FIGS. 5 and 6utilize CTS-to-Self frames and CF-end frames, these frame types are onlyexemplary and the present application is not so limited. For example,any frame or message that serves to reserve one or more channels or amedium for communication may be utilized in place of the CTS-to-Selfframes. Likewise, any frame or message that serves to clear such areservation of one or more channels or a medium may be utilized in placeof the CF-end frames.

FIG. 7 shows a flowchart of an aspect of an exemplary method of wirelesscommunication. The flowchart 700 may be used to generate and transmitany of the frames described above. The method of flowchart 700 isdescribed herein with reference to the timing diagrams 500 and 600, aspreviously described in connection with FIGS. 5 and 6. The frames may betransmitted by the AP 104 to one or more of the STAs 106 a-106 d shownin FIG. 1. In addition, the wireless device 202 shown in FIG. 2 mayrepresent a more detailed view of the AP 104, as described above. Thus,in one implementation, one or more of the steps in flowchart 700 may beperformed by, or in connection with, a processor and/or transmitter,such as the processor 204 and transmitter 210 of FIG. 2, although thosehaving ordinary skill in the art will appreciate that other componentsmay be used to implement one or more of the steps described herein.Although blocks may be described as occurring in a certain order, theblocks can be reordered, blocks can be omitted, and/or additional blockscan be added.

At block 702 the AP 104 may transmit a first message for establishing areservation of the communication medium utilizing a first combination oftransmission characteristics such that the first message is readable bya plurality of wireless devices. For example, the AP 104 may transmitthe CTS-to-Self frame 604 using a first combination of transmissioncharacteristics (e.g., at least one of a transmission frequency, aphysical layer mode, a modulation coding scheme, a number of concurrentdata streams, and a data rate) such that the STAs 106 a, 106 b, 106 cand 106 d may read (e.g., decode) the CTS-to-Self frame 604. In such anexample, at this point, the STAs 106 a-106 d will be silenced for theinterval 620.

At a block 704, the AP 104 subsequently transmits a plurality ofmessages for clearing the reservation of the communication medium, eachof the plurality of messages utilizing a different combination oftransmission characteristics than the first combination such that eachof the plurality of messages is readable by a different subset of theplurality of wireless devices, thereby sequentially clearing access toat least one communication channel of the communication medium for eachof the different subsets of the plurality of wireless devices. Forexample, the AP 104 may transmit each of the CF-end frames 606 a, 606 band 606 c sequentially and using a different combination of transmissioncharacteristics than the combination of transmission characteristicsused transmit the CTS-to-Self frame 604. The STA 106 d may read (e.g.,decode) the CF-end frame 606 a. This will clear any silence commandwithin the STA 106 d that may have been invoked by the CTS-to-Self frame604. In this way, the STA 106 d may be cleared to communicate over thecommunication medium without interference for at least the interval 630.The STA 106 c may read (e.g., decode) the CF-end frame 606 b. This willclear any silence command within the STA 106 c that may have beeninvoked by the CTS-to-Self frame 604. In this way, the STA 106 c (alongwith the STA 106 d) may be cleared to communicate over the communicationmedium without interference for at least the interval 640. The STA 106 bmay read (e.g., decode) the CF-end frame 606 c. This will clear anysilence command within the STA 106 b that may have been invoked by theCTS-to-Self frame 604. In this way, the STA 106 b (along with the STAs106 c, 106 d) may be cleared to communicate over the communicationmedium without interference for at least the interval 650.

The above implementations are compatible with legacy 802.11 wirelessSTAs and do not require any PHY or MAC changes. Moreover, a wirelessdevice instituting one or more methods herein disclosed do not requirean awareness of the number or capabilities of the surrounding STAs, asthe transmission characteristics of the frames transmitted determinewhether a particular STA will be blocked from communicating during aparticular interval.

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like. Further, a “channel width” as used herein may encompass ormay also be referred to as a bandwidth in certain aspects.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

In one or more aspects, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium.Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage media may be anyavailable media that can be accessed by a computer. By way of example,and not limitation, such computer-readable media can comprise RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium that can be used tocarry or store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Thus, in some aspects computer readable medium may comprisenon-transitory computer readable medium (e.g., tangible media). Inaddition, in some aspects computer readable medium may comprisetransitory computer readable medium (e.g., a signal). Combinations ofthe above should also be included within the scope of computer-readablemedia.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware or any combination thereof. If implemented in software, thefunctions may be stored as one or more instructions on acomputer-readable medium. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein. For certain aspects, the computer program product may includepackaging material.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method of wireless communication, comprising:generating, by a first wireless device, a first message including anindication of a first duration of blocked access to a communicationmedium and a first combination of transmission characteristics such thatthe first message is readable by a set of wireless devices; transmittingthe first message, from the first wireless device to the set of wirelessdevices, for establishing the blocked access to the communicationmedium, for the first duration, for the set of wireless devices, basedon the first combination of transmission characteristics being readableby the set of wireless devices; in response to transmitting the firstmessage, generating, by the first wireless device, a second messageincluding a second duration and a second combination of transmissioncharacteristics such that the second message is readable by a subset ofthe set of wireless devices; and transmitting the second message, withinthe first duration, from the first wireless device to the set ofwireless devices, for clearing access to the communication medium for atleast the second duration, for the subset of the set of wireless devicesbased on the second combination of transmission characteristics beingreadable by the subset of the set of wireless devices.
 2. The method ofclaim 1, further comprising repeating the transmitting the first messageand the second message according to a periodic interval.
 3. The methodof claim 1, wherein the first and second combinations of transmissioncharacteristics comprise at least one of a transmission frequency, aphysical layer mode, a modulation coding scheme, a number of concurrentdata streams, and a data rate.
 4. The method of claim 1, wherein thefirst message is a clear to send message.
 5. The method of claim 1,wherein the second message is a contention free end message.
 6. Themethod of claim 1, wherein the set of wireless devices includes at leastone wireless device not included in the subset of the set of wirelessdevices.
 7. The method of claim 1, wherein transmitting the secondmessage is further for clearing access to the communication medium, forthe subset of the set of wireless devices, for at least the secondduration and one or more successive intervals occurring within the firstduration.
 8. A device for wireless communication, comprising: aprocessor configured to: generate a first message including anindication of a first duration of blocked access to a communicationmedium and a first combination of transmission characteristics such thatthe first message is readable by a set of wireless devices; transmit thefirst message to the set of wireless devices for establishing theblocked access to the communication medium, for the first duration, forthe set of wireless devices, based on the first combination oftransmission characteristics being readable by the set of wirelessdevices; in response to transmitting the first message, generate asecond message including a second duration and a second combination oftransmission characteristics such that the second message is readable bya subset of the set of wireless devices; and transmit the secondmessage, within the first duration, to the set of wireless devices forclearing access to the communication medium for at least the secondduration, for the subset of the set of wireless devices, based on thesecond combination of transmission characteristics being readable by thesubset of the set of wireless devices.
 9. The device of claim 8, whereinthe transmitter is configured to repeatedly transmit the first messageand the second message according to a periodic interval.
 10. The deviceof claim 8, wherein the first and second combinations of transmissioncharacteristics comprise at least one of a transmission frequency, aphysical layer mode, a modulation coding scheme, a number of concurrentdata streams, and a data rate.
 11. The device of claim 8, wherein thefirst message is a clear to send message.
 12. The device of claim 8,wherein the second message is a contention free end message.
 13. Thedevice of claim 8, wherein the set of wireless devices includes at leastone wireless device not included in the subset of the set of wirelessdevices.
 14. A non-transitory computer-readable medium comprising codethat, when executed, causes a first wireless device to: generate a firstmessage including an indication of a first duration of blocked access toa communication medium and a first combination of transmissioncharacteristics such that the first message is readable by a set ofwireless devices; transmit the first message, from the first wirelessdevice to the set of wireless devices, for establishing the blockedaccess to the communication medium, for the first duration, for the setof wireless devices based on the first combination of transmissioncharacteristics being readable by the set of wireless devices; inresponse to transmitting the first message, generate a second messageincluding a second duration and a second combination of transmissioncharacteristics such that the second message is readable by a subset ofthe set of wireless devices; and transmit the second message, within thefirst duration, from the first wireless device to the set of wirelessdevices, for clearing access to the communication medium for at leastthe second duration, for the subset of the set of wireless devices basedon the second combination of transmission characteristics being readableby the subset of the set of wireless devices.
 15. The medium of claim14, wherein the code, when executed, further causes the device to repeatthe transmitting the first message and the second message according to aperiodic interval.
 16. The medium of claim 14, wherein the first andsecond combinations of transmission characteristics comprise at leastone of a transmission frequency, a physical layer mode, a modulationcoding scheme, a number of concurrent data streams, and a data rate. 17.The medium of claim 14, wherein the first message is a clear to sendmessage.
 18. The medium of claim 14, wherein the second message is acontention free end message.
 19. The medium of claim 14, wherein the setof wireless devices includes at least one wireless device not includedin the subset of the set of wireless devices.
 20. A first wirelessdevice comprising: means for generating, by the first wireless device, afirst message including an indication of a first duration of blockedaccess to a communication medium and a first combination of transmissioncharacteristics such that the first message is readable by a set ofwireless devices; means for transmitting the first message, from thefirst wireless device to the set of wireless devices, for establishingthe blocked access to the communication medium, for the first duration,for the set of wireless devices based on the first combination oftransmission characteristics being readable by the set of wirelessdevices; means for, in response to transmitting the first message,generating, by the first wireless device, a second message including asecond duration and a second combination of transmission characteristicssuch that the second message is readable by a subset of the set ofwireless device; and means for transmitting the second message, withinthe first duration, from the first wireless device to the set ofwireless devices, for clearing access to the communication medium for atleast the second duration, for the subset of the set of wirelessdevices, based on the second combination of transmission characteristicsbeing readable by the subset of the set of wireless devices.
 21. Thedevice of claim 20, wherein the means for transmitting the first messageis configured to repeatedly transmit the first message and the secondmessage according to a periodic interval.
 22. The device of claim 20,wherein the first and second combinations of transmissioncharacteristics comprise at least one of a transmission frequency, aphysical layer mode, a modulation coding scheme, a number of concurrentdata streams, and a data rate.
 23. The device of claim 20, wherein thefirst message is a clear to send message.
 24. The device of claim 20,wherein the second message is a contention free end message.
 25. Thedevice of claim 20, wherein the set of wireless devices includes atleast one wireless device not included in the subset of the set ofwireless devices.